Steam power plant and method of operating the same

ABSTRACT

The feed water is normally supplied to the steam generator to extract heat from the steam generated in the evaporator. However, at peak loads of the plant, the rate of heat extraction from the steam is temporarily reduced so that the amount of steam produced is increased with a greater flow of steam to the prime mover.

United States Patent [1 1 Dolezal I [111 Y 3,742,709 [451 July 3,1973

[ 4] STEAM POWER PLANT AND METHOD OF OPERATING THE SAME [75] Inventor: Richard Dolezal, Winterthur, I

Switzerland [73] Assignee: Sulzer Brothers, Ltd.,' Winterthur, Switzerland 221 Filed: Jan. 18, 1971 211 App]. N0.: 107,275

[30] Foreign Application Priority Data Jan. I9, 1970 Switzerland.., 676/70 [52] US. Cl. 60/106, 122/479 [51] Int. Cl. F22g 5/00, F22d 1/12 [58] Field of Search 122/479; 60/106,

[56] References Cited UNITED STATES PATENTS 3,022,235 2/1962 Brown et al. 60/105 x ll/l968 NetteL; 60/67 3,338,053 8/l968 Gorzegno eta]. 60/[05 2,526,898 l2/l950 Powell et al. l22/479 2,550,683 .5/l95l Fletcher ct al 122/479 X Primary Examiner-Martin P. Schwadron Assistant ExaminerAllen M Ostra'ger AttorneyKenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT The feed water is normally supplied to the steam generator to extract heat from the steam generated in the evaporator. However, at peak loads' of the plant,- the rate of heat extraction from the steam is temporarily reduced so that the amount of steam producedis in? creased with a greater flow of steam to the prime mover.

7 Claims, 3 Drawing Figures circulation steam generator.

STEAM POWER PLANT AND METHOD OF OPERATING THE SAME This invention relates to a steam power plant and a method of operating a steam power plant.

Briefly, the invention provides a steam power plant and a method of operating the same in which heat can be extracted at variable rates, depending on the load, from the steam generated in an evaporator of the plant by a heat transfer to the feed water supplied to the plant. Upon the occurrence of a load peak, the rate of heat extraction is temporarily reduced so that more steam can be delivered.

Generally, the steam power plant is constructed with a steam power plant a prime mover, a steam generator which is connected to supply steam to the prime mover and includes means for extracting heat from the steam generated in the evaporator of the steam generator by heat transfer to the feed water supplied to the steam generator, means for detecting peak loads on the plant,

and means for temporarily reducing the rate of extraction of heat on the occurrence of a load peak detected by the detecting means.

A control is thus provided whereby it is possible to reduce, prevent or even reverse the reduction in steam pressure immediately upstream of the prime mover which would-otherwise result from sudden load peaks,

thus permitting a rapid adaptation of the steam available to the suddenly increased steam consumption. By means of the control, good dynamic regulation of the plant can be obtained since oscillation amplitudes arising in the control systems due to load peaks canbe kept small and can be caused to decay rapidly.

The invention may be carried into practice in various embodiments, for example, as described below and as illustrated in the accompanying drawings in which:

FIG. 1 illustrates a flow diagram of a natural circulation steam generator plant; FIG. 2 illustrates a flow diagram of a forced circulation steam generator having return means for the working medium; and p v FIG. 3 illustrates a flow diagram of a modified force Referring to FIGS. 1, the power plant includes a natural circulation steam generator which is fed from a starting vessel 1 via a feed pump 2 with feed water. The steam generator essentially comprises an economizer 3, a steam and water drum 5, an evaporator8 of which the firing means. is not shown, and a superheater 10 connected to the steam space of the drum 5. The starting vessel 1 is connected through the feed pump 2-to the economizer 3 which in turn communicates through a pipeline 20 with the steam space of the drum 5. A trough 4 is located in the, drum 5 above the water level in the drum and is below the end of the pipeline 20. The through 4 also'has orifices from which thefeed water supplied thereto reaches-the water in the drum 5 in the form of streams or drops.

The pipeline 20 is provided with a three-way valve 21, the third outlet of which is connected to a branch line 22 which, while bypassing the drum 5, .terminates in a-downco'mer 6 between the drum 5 and an inlet manifold 7 connected to the evaporator 8.

nected to the live steam line 11 to measure the steam flowrate and is connected through a differentiating element 24 to the three-way valve 21. Also, a conventional three-component regulating system is provided to control the supply of feed water, that is, means for adjusting the feed water flow-rate are controlled in dependence upon the level in the drum 5, the actual rate of flow of feed water and the rate of flow of steam;

With the steam generator in normal operation, feed water is obtained by the feed pump 2 from the starting vessel 1 and is delivered through the economizer 3 and the pipeline 20 into the trough 4. The boiler water passes from the water chamber of the drum 5 through drum 5 where part of its heat is abstracted by water flowing from the trough 4. From the drum 5 the saturated steam reaches the superheater 10 and thereafter via the live steam line 1-1 passes into the turbine 12. After being expanded, the steam is precipitated in the condenser 13 and the condensate thus formed is returned by the condensate pump 14 to the starting vessel 1.

When load peaks occur, that is, if the steam consumption of the turbine 12 suddenly increases, the flowrate in the live-steam line 11 increases and causes a reduction in the steam pressure. The change in the steam flowrate is measured by the flow measuring element 23 and acts on the three-way valve 21 to'adjust the valve 21 in such a way that a greater or lesser part of the feed water from" the economizer 3-is ducted via temporary because of the differentiating element 24. In

addition, when a load peak appears a signal is transmitted to the firing system (not shown) of the steam generator to increase the firing rate. Owing to the lag in the adjustment of the firing system, the greater steam production which results from an increase of the firing rate follows on the temporary increased steam delivery due to the adjustment of the three-wayvalve 21.

Referring to FIGS. 2, wherein like reference characters indicate like parts as above, the forced flow steam generator replaces the drum 5 with a water separator 39, the lower end of which communicates with a line 25 having a circulating pump 26 by means of which condensed water is returned to the evaporator 8. Furthermore, a separate mixing vessel 27 is provided in which heat is abstracted from the saturated steam,the upper'end of the vessel being connected to the line20 which extends from the economizer 3. The lower end of the mixing vessel 27 is connected to the line 25. In this construction, the three-way valve 21' is notdisposed in the line 20 but in the connecting line 28 between the evaporator 8 and the water separator 39. A branch line 40 extends from the third outlet ofthe three-way valve 21 to the mixing vessel 27.

In addition, the superheater 10 is subdivided into two sections and a water injection line 29 leads to a point between the two superheatersec tions from the vessel 1 and contains a valve 30 which is controlled as is known in dependence upon the steam temperature near the superheater exit. The steam turbine 12 is also subdivided into two pressure stages between which there is a reheater 31.

Load peaks in the live steam line 11 are detected by a pressure measuring element 33 which communicates on the one hand through a PID controller 34 (controller with proportional integral derivative action) with a load control apparatus 35 and on the other hand communicates through a PD controller 36 with an actuator 37 which adjusts the three-way valve 21. A PI controller 38, supplied with the measured value of the rate of flow of injection water through the line 29, also acts upon the actuator 37. This quantity is measured by means of the measuring element 41. The firing system 42 of the steam plant is supplied with fueland air, for example, for the sake of simplicity, by a single pipeline 43 with a regulating valve 44. The regulating valve 44 is adjusted by the load control apparatus 35 through a controller 45. Finally, means and provided so that the rate of flow of feed water to the steam generator is regulated in relation to the level-in the water separator 39. To this end, a level measuring element 46 is connected to the separator 39 to act via a controller 47 on a regulating valve 48 upstream of the economizer 3 in the feed water supply line.

The method of operation of the steam generator is 'as follows. In normal operation the feed pump 2 delivers feed water from the starting vessel 1 via the economizer 3 into the mixing vessel 27. From the mixing vessel 27, the water passes by means of the circulating pump 26 into the evaporator 8. After discharging from the evaporator 8, the working medium is divided by means of the three-way valve 21' into two part flows. One part flow reaches the water separator 39 where entrained water is separated from the steam which then flows into the superheater 10. The separated water is returned via the line 25 into the evaporator. The other part flow is suppliedvia the branch line 40 to the mixer vessel 27 where the steam is condensed on the incoming feed water. The steam superheating in the superheater passes through the live steam line ll into the first stage of the turbine 12 and after being partially expanded therein passes into the reheater 31. The steam then flows into the second turbine stage for further expansion. The expanded steam is condensed in the condenser 13 and returned to the condensate pump 14 to the starting vessel 1.

When a load peak occurs, the pressure of the steam in the live steam line 1 1 begins to drop and this initiates a corresponding signal in the pressure measuring element33 which in turn acts upon the PD controller 36. The resultant output signal of the controller 36 acts on the actuator 37 which adjusts the three-way valve 21' so that the supply of steam via the branch line 40 to the mixer vessel 27 is temporarily reduced and, at the same time, the amount of saturated steam in the water sepa rator 39 is increased, thus preventing any. further reduction in the steam pressure in the live steam line 11. The signal delivered bythe pressure measuring element 33 also acts via the PID controller 34 on the load control apparatus 35 which increases, via the controller 45, the supply of fuel and air to the firing system 42 by a corresponding adjustment of the valve 44. The actuator 37 of the three-way valve 21' is also influenced by the rate of flow of injected water through line 29, in the sense that the quantity of steam admitted by the threeway valve 21 to the mixing vessel 27 is reduced as the flow of injected water into the superheater 10 increases. Thus, when the quantity of steam flowing into the superheater 10 is thus increased and, if the amount of heat supplied to the superheater remains the same, is superheated to a lesser extent, the amount of injected water is automatically reduced.

In one possible modification, the amount of steam flowing through the live steam line 1 l, as shown in FIG. 1, is used for. control purposes instead of the pressure of the live steam while in another possible modification the rotational speed of the turbine 12 can be used.

Referring to FIG; 3 wherein like reference characters indicate like parts as above, the forced circulation steam generator differs from that of FIG. 2 in that no separating mixing vessel is provided as a heat transfer means between the saturated steam and the feed water. Instead, the water separator 39, is used between the evaporator 8 and the superheater 10. Moreover, the three-way valve 21" is not disposed in the pipeline extending from the evaporator 8 to the water separator 39 but is disposed in the pipeline 20'which extends from the economizer 3 to the water separator 39. In this case, the branch line 60 connected to the third outlet of the three-way valve 21" extends into the water chamber of the water separator. The three-way valve 217 is adjusted by a P controller 36' whose input signal is formed from the deviation between the output delivered from an electric generator 61 and a set value for this output. The measured value of the electric power is supplied through a signal ine 62 and the set value is supplied through a signal line 63 to a junction 64 from which a signal line 65, adapted to carry the signal corresponding to the aforementioned deviation, extends to the P controller 36'. A further signal line 66, carrying the same signal, 'is connected to'a PID controller 45' which influences the firing rate by adjusting the valve 44. A purely proportional action is sufficient for the controller 36 since the integral action of the controller 45 causes the deviation between the set value-signal of the line 63 and the measured value signal of the line 62 to disappear. However, the controller 36 could be provided additionally with a differential action.

In this construction, the appearance of a sudden load peak causes the three-way valve 21"to be adjusted by the P controller 36 in such a way that more of the feed water from the economizer 3 is temporarily passed through the branch line 60 directly to the water chamber of the water separator 39 so that a smaller quantity of saturated steam is condensed and more steam is available for the turbine 12., The firing rate is simultaneously increased by means of the controller 45'. It is also possible to arrange for the application of the signal in the signal line 65 to be so powerful that the steam pressure in the live steam line '11 actually rises when the power demand is increased. A stem of this type may be particularly useful in a sliding pressure operation.

I claim: l l. A steam power plant comprising a prime mover; a steam generator connected to said prime mover to supply steam thereto; said generator including an evaporator for generating steam therein and heat extraction means for placing feed water supplied to said steam generator in heatexchange relation to the steam generated in said evaporator to condense a part of the steam;

said reducing means includes a bypass line for bypassing of at least the feed water around said heat extraction means and a valve means in said bypass line for controlling the flow of feed water through said bypass line.

4. A steam power plant as set forth in claim 3 wherein said valve is athree-way valve.

5. A steam power plant as set forth-in claim 3 wherein said steam generator is disposed to operate with natural circulation and wherein said heat extraction means is a water drum, said steam generator further including a downcomer extending from said drum to an inlet in said evaporator and a feedwater line extending to said drum to supply feed water thereto; said bypass line connecting said feedwater line to said downcomer.

6. A steam power plant as set forth in claim 3 wherein said steam generator is disposed to operate with forced circulation and wherein said heat extraction means is a water separator, connected to said evaporator to receive working medium therefrom; and which includes a feedwater line connected to a steam space in said water separator; said bypass line connecting said feedwater line to a water space in said water separator.

7. A steam power plant as set forth in claim 3 wherein said steam generator is disposed to operate with forced circulation and further includes a water separator, a first line connecting an outlet of said evaporator to said water separator and a second line connecting said water separator to an inlet of said evaporator; said bypass line connecting said'first line to' said heat extrac tion means. 

1. A steam power plant comprising a prime mover; a steam generator connected to said prime mover to supply steam thereto; said generator including an evaporator for generating steam therein and heat extraction means for placing feed water supplied to said steam generator in heat exchange relation to the steam generated in said evaporator to condense a part of the steam; detection means for detecting peak loads on said plant; and reducing means for temporarily reducing the amount of steam condensed on the detection of a load peak in said means for detecting peak loads to increase the amount of steam supplied to said prime mover.
 2. A steam power plant as set forth in claim 1 which further comprises a signal line connecting said detection means with said reducing means and a differentiating element in said signal line.
 3. A steam power plant as set forth in claim 1 wherein said reducing means includes a bypass line for bypassing of at least the feed water around said heat extraction means and a valve means in said bypass line for controlling the flow of feed water through said bypass line.
 4. A steam power plant as set forth in claim 3 wherein said valve is a three-way valve.
 5. A steam power plant as set forth in claim 3 wherein said steam generator is disposed to operate with natural circulation and wherein said heat extraction means is a water drum, said steam generator further Including a downcomer extending from said drum to an inlet in said evaporator and a feedwater line extending to said drum to supply feed water thereto; said bypass line connecting said feedwater line to said downcomer.
 6. A steam power plant as set forth in claim 3 wherein said steam generator is disposed to operate with forced circulation and wherein said heat extraction means is a water separator, connected to said evaporator to receive working medium therefrom; and which includes a feedwater line connected to a steam space in said water separator; said bypass line connecting said feed-water line to a water space in said water separator.
 7. A steam power plant as set forth in claim 3 wherein said steam generator is disposed to operate with forced circulation and further includes a water separator, a first line connecting an outlet of said evaporator to said water separator and a second line connecting said water separator to an inlet of said evaporator; said bypass line connecting said first line to said heat extraction means. 